1. Field of the Invention
This invention relates to tapchangers employed in electrical power distribution systems to maintain voltage levels of electrical power lines within predetermined ranges. More particularly, this invention provides an apparatus and method for transferring, upon detection of reverse power flow, the tapchanger control voltage input from the forward power load side to the reverse power load side of the tapchanger.
2. Description of the Background Art
In electrical power distribution systems, voltage levels on a power line tend to vary due to several factors such as the load on the power line and the power line's impedance. In order to maintain the voltage level on a power line within a predefined range or bandwidth of a fixed voltage level (e.g., 120 volts), regulators, such as load tapchanging (LTC) transformers or series regulating auto transformers using motor-driven tapchanger switches, are employed to incrementally increase or decrease the power line voltage.
Typically, tapped auto transformers comprise a tapped series winding that is operatively connected to a shunt winding by means of a tapchanging motor that rotates in either an incrementing or decrementing direction depending upon whether the regulator is used to incrementally “boost” (increase) or “buck” (decrease) the load voltage. Controllers, such as that disclosed in U.S. Pat. No. 5,581,173, the disclosure of which is hereby incorporated by reference herein, are employed to monitor the line voltage during forward power flow and, as the line voltage decreases or increases outside the predefined bandwidth, to then energize the tapchanger motor to incrementally boost or buck the line voltage to maintain the power line voltage within the predefined bandwidth of a fixed voltage level.
Due to power line topologies, forward power flow through a transformer may reverse direction. Consequently, the tapchanger must therefore operate during reverse power flow in order to properly boost or buck line voltage during such reverse power flow. Prior art tapchangers have typically calculated the source voltage according to the actual tap position and the type of regulator being used (e.g., Type A non-inverted configuration or Type B inverted configuration). Unfortunately, however, merely calculating the source voltage leads to inaccuracies in tapchanging during reverse power flow.
Therefore, it is an object of this invention to provide an improvement which overcomes the aforementioned inadequacies of the prior art tapchanger controllers and provides an improvement which is a significant contribution to the advancement of the tapchanger controller art
Another object of this invention is to provide an apparatus and method for increasing the accuracies of tapchanger controllers during reverse power flow.
Another object of this invention is to provide an apparatus and method for measuring the source side voltage during reverse power flow to assure more accurate tapchanging during reverse power flow.
The foregoing has outlined some of the pertinent objects of the invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description of the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.